The present invention relates to a semiconductor device socket and a semiconductor device connecting method, and in particular, to a semiconductor device socket and a semiconductor device connecting method using an anisotropic conductive sheet.
Recent semiconductor devices become smaller and have more pins. Accordingly, sockets are required to have terminals with smaller pitches. Thus, an anisotropic conductive sheet is often used in a contact section that electrically connects electrode terminals of the semiconductor device to corresponding electrode terminals of a substrate.
Some anisotropic conductive sheets exhibit conductivity only in their thickness direction or do so when pressed in their thickness direction. For example, a silicon rubber sheet with thin metal lines, a kind of an anisotropic conductive sheet, has a small thickness of about 1 mm. Thus, the silicon rubber sheet is more unlikely to pick up external noise than sockets using spring pins. Consequently, the silicon rubber sheet can accommodate higher clock speed.
However, the anisotropic conductive sheet has much larger coefficient of thermal expansion than semiconductor devices and substrates. Accordingly, heat generated by the semiconductor device operation expands and deforms the anisotropic conductive sheet. This may cause a position gap between the anisotropic conductive sheet and the substrate. In particular, if the semiconductor has terminals with a very small interval such as bare chips, the position gap of the anisotropic conductive sheet from substrate, resulting from the thermal expansion and deformation, is not negligible.
FIG. 6 is a sectional view showing the structure of a conventional semiconductor device socket. A conventional socket 200 has a base plate 5 (support member) on which a substrate 3 is placed, and an anisotropic conductive sheet 2 that electrically connects electrode terminals 10 of the semiconductor device 1 to the corresponding electrode terminals 8 of the substrate 3 placed on the base plate 5. Furthermore, the conventional socket 200 includes a socket frame 9 (guide member), which is provided around the anisotropic conductive sheet 2, to put the semiconductor device 1 in, a pressure plate 4 that presses the semiconductor device 1 along the socket frame 9 from above, and screws 6 used to fix the members of the socket.
In this conventional socket 200, the semiconductor 1 and the substrate 3 are sandwiched between the pressure plate 4 and the base plate 5 to contact the terminals 10 of the semiconductor 1 with the pads 8 (electrode terminals) on the substrate 3 via the anisotropic conductive sheet 2.
FIG. 7 is an enlarged sectional view showing the contact portion in FIG. 6. FIG. 7a shows a state before the semiconductor device starts to operate. FIG. 7b shows a state where the semiconductor device 1 is in operation and generating heat. FIG. 7c shows that heat generated in the semiconductor has caused a positional gap.
The anisotropic conductive sheet 2 is a silicon rubber sheet in which a plurality of thin metal lines 11 that are conductive lines are buried. The thin metal lines 11 electrically connect the terminals 10 of the semiconductor device 1 and the corresponding pads 8 of the substrate together.
FIG. 7a shows a state in which the anisotropic conductive sheet 2 and the substrate 3 are not heated. The terminals 10 of the semiconductor device 1 are connected normally to the corresponding pads 8 of the substrate 3 via the anisotropic conductive sheet 2.
When the semiconductor device 1 begins to operate, the temperatures of the anisotropic conductive sheet 2 and the substrate 3 are increased by heat generated by the device 1. The increase in temperature starts to expand the anisotropic conductive sheet 2 and the substrate 3 as shown in FIG. 7b. 
The anisotropic conductive sheet 2 has a much large coefficient of thermal expansion than that of the substrate 3. Thus, position gap is generated between the thin metal lines 11 and the pads 8 of the substrate 3. It may result in short-circuiting the adjacent terminals or connecting the thin metal line 11 to the incorrect pad 8 in the end as shown in FIG. 7c. In particular, if the semiconductor device 1 is formed as a bare chip, the space between the adjacent terminals 10 is very small. Consequently, position gap has a great possibility to cause a short circuit or incorrect connection.
In the description of FIGS. 6 and 7, the anisotropic conductive sheet 2 is an elastic rubber sheet in which the plurality of thin metal lines 11 are buried. Description will be given of another example in which the anisotropic conductive sheet 2 is composed of conductive particles arranged in elastic rubber.
FIG. 8 is an enlarged sectional view showing the contact portion. FIG. 8a shows a state before an operation of the semiconductor device starts. FIG. 8b shows a state where the semiconductor device 1 is in operation and generating heat. FIG. 8c shows that heat generated in the semiconductor has caused a positional gap.
The anisotropic conductive sheet 2 is a silicon rubber sheet composed of a plurality of metal particles 20 arranged in silicon rubber. The pressure plate 4 is used to press the semiconductor device 1 to push the terminals 10 of the semiconductor device 1 into the anisotropic conductive sheet 2. The metal particles 20, which are pushed by the terminals 10, contact with one another to electrically connect the terminals 10 of the semiconductor device 1 to the corresponding pads 8 of the substrate.
FIG. 8a shows a state where the anisotropic conductive sheet 2 and the substrate 3 are not heated. The terminals 10 of the semiconductor device 1 are connected normally to the corresponding pads 8 of the substrate 3 via the anisotropic conductive sheet 2.
When the semiconductor device 1 starts to operate, however, the device 1 itself generates heat resulting in increasing the temperature of the anisotropic conductive sheet 2 and substrate 3. The increase in temperature causes to expansion of the anisotropic conductive sheet 2 as shown in FIG. 8b. This expansion results in positional gap between the metal particles 20 and the pads 8 of the substrate 3 as shown in FIG. 8c. This may cause the adjacent terminals to be short-circuited.